Please use this identifier to cite or link to this item: https://hdl.handle.net/10419/268860 
Year of Publication: 
2023
Series/Report no.: 
Working Paper No. 426
Publisher: 
University of Zurich, Department of Economics, Zurich
Abstract: 
This paper explores an algebraic relationship between two types of coefficients for a regression with several predictors and an additive binary group variable. In a general regression, the regression coefficients are allowed to be group-specific, the restricted regression imposes constant coefficients. The key result is that the restricted coefficients imposing homogeneity are not necessarily a convex average of the unrestricted coefficients obtained from the more general regression. In the context of treatment effect estimation with several treatment arms and grouplevel controls, this means that the estimated effect of a specific treatment can be non-zero, and statistically significant, even if the estimated unrestricted effects are zero in each group.
Subjects: 
Ordinary least squares
subsample heterogeneity
variance-weighting
average treatment effect
JEL: 
C21
Persistent Identifier of the first edition: 
Document Type: 
Working Paper

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